Freezing Aristichthys Nobilis Preservation Technology Research

Freshness is the main quality indicator of freshwater fish, it is the major factor to decide the price. However, due to the high moisture and protein content, the freshness of freshwater fish is easier to decline after their death, corrupting rapidly, so it is necessary to study the effective preservation techniques of fish. In this paper, we studied the change of the microflora during partialfrozen storage of Aristichthys nobilis and analysed applicative prospect of the natural preservatives in freshwater fish storage, which to provide technical support and theoretical basis for the preservation of freshwater fish. Research methods and results were as follows:1A total of497bacteria strains were isolated from Aristichthys nobilis and identified as:Pseudomonas, Plesiomonas, Edwardsiella, E.cloacae, Acinetobacter, Flavobacterium, Corynebacterium, Lactococcus, Kurthia, Staphylococcus. It was found that Pseudomona, Corynebacterium, Kurthia and Staphylococcus were the main microorganisms in the early stage of storage. The proportion of gram-positie and gram-negative bacteria was nearly1:1. However, in the later stage of partial frozen storage, the dominant bacterias were Pseudomona and Acinetobacter, the ratio of Pseudomona was50%of the total dominant bacterias, the gram-negative bacteria was about85%. According to the molecular idengtification, Pseudomonas were mainly fluorescence pseudomonas. Based on the total bacteria count, the shelf life were about20～25days during partial frozen storage.2The antimicrobial activity of the natural preservatives on spoilage baeteria from fish meat was determined by using agar diffusion method. Three natural preservatives had different inhibition on the six different strains(Pseudomona, Acinetobacter, Plesiomonas, Corynebacterium, Kurthia, Staphylococcus), and the inhibition effect was revelant to the concentration of preservatives. The antimicrobial activity of30million chitosan was the best among three different molecular weights, the optimal concentration was lOg/L.And the inhibition effect was better for Pseudomonas and Acinetobacter. The inhibition effect of tea polyphe-nols was better for Plesiomonas and Corynebacterium, when the concentration of tea polyphenols was4g/L, the square of bacteriostatic circle was125.05mm2and125.03mm2respectively. However, Nisin can only inhibit the gram-positive bacteria, when the concentration was3g/L, the square of bacteriostatic circle was145.05mm2and150.15mm2 respectively for Staphylococcus and Corynebacterium.3The fresh-keeping effect of the natural preservatives was evaluated on the partial frozen fish by measuring sensory changes, the total bacteria count, TVB-N value, pH value and TBARS value. According to the results, chitosan was the best choice for keeping fish fresh based on single factor experiments, optimal concentration was10g/L, the shelf life of fillet were about30days. Through the orthogonal experiment design, the optimized combination was20min ultraviolet irradiation,10min ultrasonic treatment,10min soaking. By the verification, the shelf life of fillet were about38days after orthogonal experimental design.4The combination of the natural preservatives for the preservation was optimized by response surface experiment design. The antimicrobial effect of preservatives in preservation solution was tea polyphenols> Nisin> chitosan, it was a significant synergy with one another of the three natural preservatives.The optimum proportion of the combination of chitosan, tea polyphenols, Nisin was13.08g/L、3.00g/L and1.72g/L respectively. The relative error of modle was1.81%, and showed the regression model better credibility. Based on the TVB-N value, the shelf life of fish with compound preservatives were about50days during partial frozen storage.